JP3470622B2 - Nitride semiconductor light emitting device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using a nitride semiconductor and capable of emitting longer wavelength light, and more particularly to a light emitting device which is highly reliable and capable of emitting long wavelength light with high brightness.

[0002]

2. Description of the Related Art Today, there is a light emitting element using a nitride semiconductor as a semiconductor material capable of emitting high brightness from ultraviolet to red as a material of a light emitting element. In particular, a light emitting device capable of emitting ultraviolet rays and a light emitting device capable of emitting blue, blue-green, green, etc. capable of emitting ultra-high brightness of 1000 mcd or more have been developed and have begun to be used as full-color or multi-color LED displays. There is. At present, it is extremely difficult to form a light emitting element that emits yellow or red light having a longer wavelength with high brightness by using a nitride semiconductor. Therefore, it is difficult to form a red light emitting layer using GaP, AlGaInP, GaAsP or the like as a light emitting layer material. The present situation is to realize a full-color display and the like in combination with a light emitting element capable of emitting yellow light with high brightness.

However, when light emitting elements capable of emitting RGB (red, green, blue) light are formed from different semiconductor materials,
Various characteristics such as electrical and optical are different depending on the semiconductor material. For example, nitride semiconductors currently have higher driving voltage than light emitting devices using other semiconductor materials. Therefore, when light emitting elements having different semiconductor materials are used at the same time, they must be designed separately from the power supply voltage. Further, the luminous intensity changes with temperature rise and cooling, but the characteristics remarkably differ depending on the semiconductor material. Therefore, there is a strong demand for a semiconductor light emitting device that can emit various emission spectra such as red, which is a long wavelength of visible light, from ultraviolet region to high output, using the same semiconductor material.

An example of a light emitting device using a nitride semiconductor for the light emitting layer is shown in FIG. This light emitting element can emit light up to green, which is the short wavelength side of visible light, with high brightness. Specifically, on the sapphire substrate 213, GaN, AlN, G
A buffer layer 208, n formed of aAlN or the like at a low temperature
Base layer 2 for forming a contact layer on which a mold electrode is formed
07, a contact layer 206 on which an n-type electrode is formed, a multilayer film 205 modulation-doped with n-type impurities, an active layer having a multiple quantum well structure by alternately stacking a GaN 203 that serves as a barrier layer and an InGaN 202 that serves as a well layer. Are formed. On the active layer, a multilayer film 204 of AlGaN and GaN doped with Mg, which is a p-type dopant, is used as a p-type clad layer, and G doped with Mg is used as a p-type contact layer.
The aN layer 209 is laminated. A light emitting device can be formed by exposing the p-type and n-type contact layers and then forming the electrodes 210, 211, and 212 on the contact layers, respectively.

Since the emission spectrum emitted from the light emitting device depends on the band gap of the semiconductor forming the active layer, which is the light emitting layer, by increasing the amount of In contained in the active layer, semiconductor light emission of longer wavelength is achieved. The element can be constructed. In addition, AlG is formed on at least one of the light emitting layers.
The emission wavelength can be lengthened by forming aN. In particular, by increasing the amount of Al, a semiconductor light emitting device having a longer wavelength can be constructed.

[0006]

However, as the amount of In contained in the light emitting layer increases, the crystallinity of the nitride semiconductor tends to significantly decrease. Therefore, in a nitride semiconductor light emitting device that emits a spectrum of wavelengths longer than green, there arises a problem that the brightness is extremely lowered or no light is emitted. Similarly, as the Al mixed crystal ratio of the AlGaN layer formed on at least one of the light emitting layers is increased,
Depending on the usage environment, there is a problem that the output is reduced or no light is emitted. In particular, it becomes a big problem in the light emitting element which has begun to be used in various fields as the usage is expanded. Therefore, the present invention is to provide a nitride semiconductor light emitting device capable of emitting a light emission spectrum having a longer wavelength than that of green light in visible light with high reliability and high brightness.

[0007]

A nitride semiconductor device according to the present invention is provided with an I-type between a p-type nitride semiconductor and an n-type nitride semiconductor.
A nitride semiconductor light emitting device having an active layer containing a nitride semiconductor containing n and Ga, wherein the nitride semiconductor light emitting device comprises an n-type nitride semiconductor side and a p-type nitride semiconductor side of the active layer. At least one of them has a B _x Ga _(1-x) N layer (where 0 <x ≦ 1), and the active layer has a quantum well structure composed of GaN and InGaN, and both ends thereof. Is GaN. In addition, an n-type nitride semiconductor, In, and Ga are sequentially arranged from the substrate side.
A nitride semiconductor light emitting device comprising: an active layer including a nitride semiconductor including: and a p-type nitride semiconductor, wherein the nitride semiconductor light emitting device is on the p-type nitride semiconductor side of the active layer. A B _x Ga _(1-x) N layer (where 0 <x ≦ 1), and a B _x Ga _(1-x) N layer on the n-type nitride semiconductor side of the active layer. It is characterized by not having (however, 0 <x ≦ 1). This makes it possible to construct a nitride semiconductor light emitting device capable of emitting a longer wavelength emission spectrum while maintaining the crystallinity of the light emitting layer, and at the same time, capable of emitting high brightness light for a long period of time even under high temperature and high humidity. Reliability can be maintained as a semiconductor light emitting device.

[0008]

DETAILED DESCRIPTION OF THE INVENTION As a result of various experiments, the present inventor
By forming a specific nitride semiconductor layer on at least one of the light emitting layers containing a nitride semiconductor containing n and Ga, the wavelength becomes longer than the theoretical value of the emission wavelength calculated from the band gap of the light emitting layer. The inventors have found that the light-emitting element can be manufactured with high reliability and can complete the present invention.

That is, although the effect of the present invention is not clear, the emission wavelength emitted from the light emitting element can be made longer by disposing a specific layer made of a homologous element having a different lattice constant in at least one of the light emitting layers. It can be on the wavelength side. It was also found that, when the concentration of the element forming the specific layer is increased in order to make the wavelength longer, some elements have a great influence on the characteristics such as reliability of the light emitting element.

When GaAlN is formed on at least one of the light emitting layers, the wavelength can be made longer than the theoretical value of the light emission wavelength calculated from the band gap of the light emitting layer. Therefore, the Al content may be increased in order to form a light emitting device having a longer wavelength.

However, when the Al content of the GaAlN layer formed on at least one of the light emitting layers is increased in order to make the theoretical light emission wavelength emitted from the active layer longer, a nitride formed is formed. The brightness of a semiconductor light emitting element tends to drastically decrease under high temperature and high humidity. This is due to the sudden increase of GaAlN due to oxidation caused by the intrusion of oxygen from the outside.
It is considered that the film quality of the layer deteriorates. The applicant is Ga
Stable B _x G even under high temperature and high humidity than AlN layer
By providing the a _(1-x) N layer on at least one of the active layers, the emission wavelength of the nitride semiconductor light emitting device can be made longer while maintaining reliability.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail, but it goes without saying that the present invention is not limited thereto.

(Example 1) A light emitting device made of the nitride semiconductor of the present invention was formed into a film on a sapphire substrate which had been previously cleaned by MOCVD. In addition to the sapphire substrate, various substrates such as spinel, gallium nitride single crystal, and silicon carbide can be selected as the substrate on which the nitride semiconductor is formed, as desired. First, a sapphire substrate is placed in a reaction vessel of an MOCVD apparatus and baked at 800 ° C. while flowing hydrogen gas for cleaning.

Next, TMG (trimethylgallium) gas as a source gas, ammonia gas, and nitrogen gas as a carrier gas were made to flow, and GaN was deposited as a buffer layer on the sapphire substrate at a substrate temperature of 550 ° C. with a thickness of 150 Å. The buffer layer is provided to improve the crystallinity of the nitride semiconductor layer formed on the buffer layer.
Besides N, AlN or GaAlN can be formed at a low temperature.

After forming the buffer layer, the flow of the raw material gas is stopped, the film forming temperature is raised to 1050 ° C., and TMG, ammonia gas and nitrogen gas as the carrier gas are made to flow again to make the n-type GaN layer 1 thick. The film was formed to a thickness of 0.5 μm.

Then, an n-type GaN layer for forming an n-type electrode is formed on the n-type GaN. While maintaining the film forming temperature, TMG, ammonia gas as a source gas, nitrogen gas and a silane gas as a carrier gas were flown to produce n ⁺ type Ga.
A film of N having a thickness of 2.3 μm was formed.

N ⁺ type GaN while maintaining the film formation temperature
TMG as a source gas, nitrogen gas, and hydrogen gas as a carrier gas are flown thereover to form undoped GaN and Si-doped GaN in 20 cycles, respectively. Note that Ga
The N layer is a modulation dope having different impurity concentrations of Si, which is an n-type impurity.

Next, as a specific layer of the present invention, a BGaN layer for introducing strain into the active layer is formed to a thickness of 100 Å. The film thickness is set to 1050 ° C., the source gas is TMG, ammonia gas, TEB (triethylboron) gas, and nitrogen gas and silane gas are flown as a carrier gas to give a thickness of 1
A B _0.2 Ga _0.8 N layer of 00Å is deposited. The strain introduction layer of the present invention is smaller than the average thermal expansion coefficient of the active layer, and the emission wavelength can be made longer by forming it on at least one of the active layers. In order to introduce distortion into the active layer, the emission wavelength from the light emitting element can be made longer by increasing the content of B if the thickness is the same. Similarly, if the composition is the same, the emission wavelength emitted from the light emitting element can be made longer by increasing the film thickness.

Therefore, the B _x Ga.sub. _(1-x) N layer can be thickened as long as the crystallinity of the nitride semiconductor such as the active layer formed thereon is not impaired. Specifically, it is preferably 5Å to 1000Å, more preferably 20Å to 2
It is 50Å. Similarly, the composition ratio of B can be 0 <x ≦ 1, but more preferably 0 <x ≦ 0.4.
In the present invention, more preferably, when 0.1 ≦ x ≦ 0.3, it is possible to configure a nitride semiconductor light emitting device that does not deteriorate the crystallinity and reliability.

Subsequently, on the B _0.2 Ga _0.8 N layer, an active layer having a multiple quantum well structure in which 250 Å GaN and 30 Å thickness of InGaN are repeated 6 cycles as an active layer, and GaN is formed at both ends is formed.

Specifically, while maintaining the film formation temperature at 1050 ° C., TMG gas as a source gas, ammonia gas, and nitrogen gas as a carrier gas are flown on the modulation-doped GaN layer to form an undoped GaN film at 30 Å. Let Then, the film forming temperature is lowered to 800 ° C. while flowing only the carrier gas. TMI (trimethylindium) gas, TMG gas, nitrogen gas as a source gas, and hydrogen gas as a carrier gas were flown to obtain undoped In
_A film of _0.8 Ga _0.2 N is formed at 250 Å. After repeating this 6 cycles, the film forming temperature is finally set to 1050 ° C., TMG gas as a source gas, ammonia gas and nitrogen gas as a carrier gas are caused to flow to form an undoped GaN film at 30 Å to form an active layer. In this example, a nitride semiconductor light emitting device having a multiple quantum well structure will be described. InGaN layers and the like having a thickness of about 3 nm are used as In layers.
It can also be used in a nitride semiconductor light emitting device as a light emitting layer having a single quantum well structure containing. The present invention can also be used in a light emitting device capable of emitting multicolor light in which the In composition of the well layer in the multiple quantum well structure is made different. In this case, it is preferable to provide the B _x Ga _1-x N layer on the well layer side where it is desired to emit longer wavelength light. Further, in the present invention, when the composition ratio of In increases, it becomes extremely difficult to form a light emitting layer, so In _a Ga _{1 -a} N
In particular, when the composition ratio a of In is larger than 0.5, the effect is particularly remarkable.

Next, the above-mentioned B _0.2 Ga _0.8 N layer was formed to a thickness of 2 without introducing silane gas, which is an n-type impurity, on the active layer.
It is formed in the same manner except that it is set to 0Å. Although the impurities that determine the conductivity type are not introduced here, it is also possible to introduce n-type and p-type impurities as desired. When the B _x Ga _1-x N layer is formed in contact with the active layer, it can be made non-doped in order to prevent excessive impurities from being introduced into the active layer. On the other hand, when non-doped, the short-circuit current is reduced and the withstand voltage is improved, but since the resistance component increases, various impurity elements can be added as desired. The B _x Ga _1-x N layer may be doped with an impurity element of each conductivity type, for example, Mg that becomes a p-type impurity.
And Si that is an n-type impurity may be mixed at the same time. Further, instead of being uniformly distributed in the layer, it is possible to dope the composition ratio in a gradient direction by placing it in the film thickness direction. Further, it may be provided between well layers forming the light emitting layer, if desired. Further, as long as they do not impair the weather resistance BGaN layer may further contain a Al and _{B x Al y Ga 1-xy} N layer. In this case, by setting the Al composition ratio y <0.2, it is possible to maintain the weather resistance to some extent while making the wavelength longer. Unless otherwise specified in the present invention does not exclude a case containing Al in B _x Ga _1-x N layer. Similarly, other elements can be mixed as long as the wavelength resistance is maintained and the weather resistance is maintained.

Subsequently, the p-type clad layer has a thickness of 40Å
Then, a superlattice p-type clad layer is formed by repeating Mg-doped AlGaN and Mg-doped InGaN with a thickness of 25 Å five times. While maintaining the film formation temperature at 1050 ° C., TMG gas, TMA (trimethylaluminum) gas, ammonia gas as a source gas, nitrogen gas as a carrier gas, and Cp ₂ Mg (cyclopentadienyl magnesium) gas as a p-type dopant are used. It is introduced to form p-type AlGaN at 40 Å.

Finally, while maintaining the film formation temperature at 1050 ° C., TMG gas, ammonia gas, nitrogen gas as a carrier gas and Cp ₂ Mg as an impurity gas are flown as a source gas to form a Mg-doped GaN film as a p-type contact layer. Let

After forming the nitride semiconductor wafer, the active layer and the like are removed by RIE (reactive ion etching) so that the n-type contact layer can be partially exposed. Then, p-type and n-type electrodes are formed on the p-type and n-type contact layers by sputtering. Note that p
A transparent electrode and a p-type pad electrode formed thereon are formed on the mold contact layer. The nitride semiconductor wafer is scribed to form each LED chip.

The light emitting device thus formed as shown in FIG. 1 can be formed as a light emitting device capable of emitting light having a wavelength longer than the emission wavelength theoretically calculated from the composition ratio of In contained in the light emitting layer. it can.

(Comparative Example 1) In Example 1, B _0.2 G
A light emitting device was formed in the same manner except that an AlGaN layer was formed instead of the a _0.8 N layer. A light emitting device having a main emission peak of about 580 nm, which is an emission wavelength for both, was formed.
At this stage, the brightness of the nitride semiconductor light emitting device using the BGaN layer was 1.7 times or more that of the nitride semiconductor light emitting device using the AlGaN layer. At this time, the composition ratio x of B was 0.2 and the composition ratio y of Al was 0.2.

While supplying power to each light emitting element,
RH60, 1h and 80 ℃, RH50, 1h 1000
Cycled and weathered on average of 1000 pieces
It was B _0.2Ga_0.8Al instead of N layer_0.2Ga_0.8N layers
Approximately 70% of the light emitting elements used in the comparative example cannot emit light.
However, the light emitting element of the present invention emits no light.
The device was only 3%. With this
The bright light emitting element can emit long wavelength light and
It can be seen that this is a highly reliable nitride semiconductor light emitting device.

(Example 2) In Example 1 of the present invention,
Instead of the B _0.2 Ga _0.8 N layer below the active layer, B _0.1 Ga _0.9 N
A nitride semiconductor light emitting device was formed in the same manner as in Example 1 except that the B _0.2 Ga _0.8 N layer on the active layer was not formed using the layer. The light emitting device of Example 2 had a shorter wavelength than that of Example 1, but showed excellent weather resistance as in Example 1.

Example 3 In Example 1 of the present invention,
The B _0.2 Ga _0.8 N layer below the active layer is not formed, and 250 Å B _0.4 Ga _0.6 N is used instead of the B _0.2 Ga _0.8 N layer above the active layer.
A nitride semiconductor light emitting device is formed in the same manner as in Example 1 except that the layers are used. The light emitting device of Example 3 has a longer wavelength than that of Example 2, and exhibits excellent weather resistance as in Examples 1 and 2.

[0031]

According to the present invention, B _x Ga _(1-x) N is formed in at least one of the light emitting layers containing In in the nitride semiconductor light emitting device.
By providing the layer, it is possible to emit an emission spectrum having a wavelength longer than the theoretical value considered from the In composition ratio,
In addition, a highly reliable nitride semiconductor light emitting device can be obtained regardless of the use environment.

[Brief description of drawings]

FIG. 1 shows a schematic cross-sectional view of a nitride semiconductor light emitting device of the present invention.

FIG. 2 is a schematic cross-sectional view of a nitride semiconductor light emitting device shown for comparison with the present invention.

[Explanation of symbols]

100 ... formed on the light emitting layer _{B x Ga (1-x)} B is formed below the N layer 101 ... light-emitting layer _x Ga _(1-x) N layer 102, ... light-emitting layer A well layer 103 constituting a light-emitting layer, a barrier layer 104 constituting a light-emitting layer, a p-type cladding layer 105, a multi-layer film 106 in which an n-type impurity is modulation-doped, and a contact in which an n-type electrode is formed. Layer 107 ... Base layer 108 forming a contact layer on which an n-type electrode is formed ... Buffer layer 109 ... P-type contact layer 110 ... Translucent electrode 111 ... P-type pad electrode 112 ... n-type pad electrode 113 ... sapphire substrate 202 ... well layer 203 forming a light-emitting layer ... barrier layer 204 forming a light-emitting layer ... p-type clad layer 205 ... n-type impurities Modulation-doped multilayer film 206 ... An n-type electrode is formed. Contact layer 207 ... Base layer 208 for forming contact layer on which n-type electrode is formed ... Buffer layer 209 ... P-type contact layer 210 ... Translucent electrode 211 ... P-type pad Electrode 212 ... N-type pad electrode 213 ... Sapphire substrate

Claims (2)

(57) [Claims] 1. A nitride semiconductor light emitting device having an active layer containing a nitride semiconductor containing In and Ga between a p-type nitride semiconductor and an n-type nitride semiconductor, wherein the nitride semiconductor light emission is performed. The device has B _x on at least one of an n-type nitride semiconductor side and a p-type nitride semiconductor side of the active layer.
It has a Ga _(1-x) N layer (where 0 <x ≦ 1), and the active layer has a quantum well structure composed of GaN and InGaN, and both ends thereof are GaN. A characteristic nitride semiconductor light emitting device. 2. An n-type nitride semiconductor, in order from the substrate side,
An active layer containing a nitride semiconductor containing In and Ga;
a p-type nitride semiconductor, a nitride semiconductor light emitting device having the nitride semiconductor light emitting device, the p-type nitride semiconductor side _{B x Ga (1-x)} N layer of the active layer (where 0 <x ≦ 1
B _x Ga _(1-x) N layer (where 0 <x ≦ 1 ₎ on the n-type nitride semiconductor side of the active layer.
The nitride semiconductor light emitting device is characterized in that